Understanding Insects in Stored Grains What Farmers and Consumers Need to Know
Insects in stored crops, like wheat, corn, oats, barley, and soybeans can cause significant issues for both farmers and consumers. For farmers, insect infestations in grain bins can lead to economic losses from shrink and reduced product quality. For livestock and horse owners, insects from commercial grain in feeds can reduce nutrients and palatability of feed as well as infest their barns. For consumers, the presence of insects in food storage and handling may raise concerns about food safety and quality especially when chemical techniques are used to control pests that may result in pesticide residues in food. Lets explore common insect pests in grain storage, control methods, and the economic and quality impacts of insect damage on food and feed.
Common Insects Found in Stored Cereal Crops
Several types of insects are commonly found in stored grains, each with its own characteristics and effects on crop quality. Below are some of the most frequently encountered pests:
- Granary Weevil (Sitophilus granarius)
- These small beetles are internal feeders, meaning their larvae develop inside the grain kernels, causing significant internal damage.
- Rice Weevil (Sitophilus oryzae)
- Similar to the granary weevil, rice weevils are also internal feeders and are particularly problematic in stored grains like rice, corn, and wheat.
- Red Flour Beetle (Tribolium castaneum)
- These beetles primarily feed on broken or processed grains, and their larvae can contaminate the product with waste, reducing its quality.
- Sawtoothed Grain Beetle (Oryzaephilus surinamensis)
- This insect feeds on a variety of stored grains and can rapidly reproduce, leading to large infestations.
- Indian Meal Moth (Plodia interpunctella)
- The larvae of these moths spin silk webs in stored grain, which can lead to clumping and contamination.
- Lesser Grain Borer (Rhyzopertha dominica)
- A destructive pest of stored grains, the lesser grain borer feeds both on whole and processed grains, often causing severe damage to stored cereal crops.
Economic and Quality Impact of Insect Damage
Insects can cause major economic losses to farmers by reducing both the quantity and quality of stored cereal crops. Damage from feeding, contamination by insect waste, and moisture buildup from infestation can lead to spoilage and mold growth. Additionally, insects can reduce the nutritional value of grain, which impacts feed quality for livestock and food quality for pets and humans.
In terms of the economic impact, value of grain losses from insects in storage can range from 5% to 10%, depending on the severity of the infestation. For farmers, this means reduced profits and, in some cases, the need to discard affected crops entirely. Insects also lead to increased storage costs because of the need for regular treatments and monitoring. Insects in stored grain bins can lead to grain weight losses of up to 10–20% within the first three to six months of storage. One common pest, the greater grain weevil, is known to cause substantial damage, with storage pests responsible for an estimated 63.85% of grain weight loss. On a global scale, it’s estimated that insects and other pests contribute to post-harvest grain losses of 10–40%, depending on the region and storage conditions. In developed countries, where storage conditions and pest control methods are more advanced, losses are typically lower, averaging around 9%. However, in regions with less infrastructure, such as parts of the developing world, post-harvest losses can exceed 20%. The annual global cost of losses due to insect pests in stored grain is estimated to be around $100 billion. This includes not only the direct loss of crops but also the costs associated with reduced grain quality, contamination, and the additional expenses required for pest control measures.
For consumers, insect infestations can lead to concerns about food safety and product quality, particularly if insect fragments or contaminants are found in processed products. Even small infestations can have a significant impact on consumer trust and marketability. Additionally, homeowners purchasing and storing feed for wild birds, wildlife or livestock near their homes can introduce pests into their pantry causing infestation of their own food supply and kitchen storage areas.
Basic Control Methods for Grain Insects
To prevent insect infestations in grain bins, proper management and storage practices are key. Here are some general control methods that farmers can adopt:
- Sanitation
- Thoroughly clean grain storage areas and bins before filling them with fresh crops. Remove all old grain and residues that can harbor insects. Sweep all areas, seams, clean all webbing, hollow ladders and outside areas around the bin removing even weeds and vegetative matter that can harbor insects. If necessary dust or fumigate the empty unit.
- Avoid putting new crop on top of old crop. Any infestation will only get worse and be more difficult to eradicate.
- Proper Drying and Aeration
- Maintain proper moisture levels in stored grains. Dry grain to 13% moisture or lower, as higher moisture levels create favorable conditions for insect reproduction. Regular aeration also helps to keep grain cool and dry, which discourages insect activity. Keep air circulating until temperatures drop below 50F when insects will stop feeding and reproducing.
- Monitoring and Inspection
- Regularly inspect grain bins for signs of insect activity. Use pheromone traps and temperature probes to monitor for potential infestations early on.
- Insecticides and Insect Growth Regulators (IGRs)
- In addition to fumigation, various products can be applied while filling or emptying grain bins to prevent or control insect infestations.
Insecticides and Insect Growth Regulators (IGRs)
Insecticides and insect growth regulators (IGRs) offer an alternative or supplementary control method for managing insects in stored grain. IGRs are very safe and only affect insects by stopping the development of larvae at a certain stage. While IGRs are not an immediate kill, the interruption of the life cycle is an option to help keep them in check. These products can be applied directly to the grain during loading or unloading or dusting empty storage units before refilling, helping to reduce infestations and prevent future pest development. Insecticides should be handled with appropriate PPE and safety precautions. One product available at The Mill that combines both insecticides and an IGR is:
Gravista-D
- What It Is: Gravista-D is a combination of insecticides and an insect growth regulator that can be applied as a dust treatment to grain as it enters the storage bin. It targets a variety of insect pests and works by killing adult insects while also preventing the development of larvae.
- How It Works: The insecticide kills insects on contact, while the IGR component prevents insect larvae from maturing into adults, breaking the life cycle of pests.
- Usage: Farmers can apply Gravista-D during grain handling to ensure that newly stored grain is protected from pests.
- Benefits: Provides long-lasting protection against a broad range of insects.
- Safety: When applied at label instructions, Gavista-D does not require special licensing to use and is safe to handle with appropriate gear and handling practices. IGRs are safe for humans and pets. Some grain protectants with insecticides may result in very low residues, so check with the buyers that they will be marketable.
Natural Alternatives
Diatomaceous Earth (DE) has been used in grain storage areas to keep insect infestations under control. DE is a natural and effective option for controlling insects in stored grains. It's made from fossilized remains of diatoms, a type of microscopic algae, and is composed of silica. DE works by physically damaging the exoskeletons of insects, leading to their dehydration and eventual death. This method is favored by farmers and grain handlers because it is non-toxic to humans and animals, leaving no harmful chemical residues.
- Mechanism: DE has sharp, microscopic edges that pierce the protective outer layer of insects, causing them to lose moisture and die from dehydration.
- Effective Against: DE is effective against a wide range of common grain storage pests, including weevils, beetles, and moths.
- Long-Lasting: Once applied, DE remains effective as long as the grain is kept dry, making it a suitable long-term preventative measure.
Application in Grain Storage:
- Direct Mixing: Diatomaceous earth is mixed with the grain as it is loaded into storage bins. Typically, 1-2 pounds of DE are used per ton of grain, though this can vary depending on grain type and infestation risk.
- Dusting: DE can also be applied as a surface dust in grain bins or storage areas. This helps prevent pests from entering or infesting the grain from the top.
- Perimeter Treatment: In addition to being mixed with grain, DE can be applied around the perimeter of storage areas as a preventative barrier.
Advantages of Diatomaceous Earth:
- Non-Toxic: DE is safe for humans and animals, making it a great option for organic or chemical-free grain storage.
- No Residues: Unlike chemical insecticides or fumigants, DE leaves no harmful residues and does not affect the grain’s quality for food or feed.
- Resistance: Insects do not develop resistance to DE, making it a reliable, long-term solution for pest control.
- Ease of Use: DE is relatively easy to apply, requiring minimal specialized equipment.
Challenges:
- Moisture Sensitivity: Diatomaceous earth loses its effectiveness in moist environments. To ensure it works properly, grain must be kept dry, and the DE must be applied to dry grain.
- Mechanical Irritation: Though non-toxic, DE can irritate the eyes, skin, and respiratory systems of workers if not handled properly. Workers should use protective gear, such as masks and gloves, during application.
Effectiveness:
Studies and field use have shown that DE can reduce pest populations significantly in stored grain when applied correctly. Its ability to provide a physical barrier rather than relying on chemical toxicity means it can be safely used in organic storage systems or in situations where chemical use is restricted.
Fumigation: Techniques, Chemicals, and Concerns
Fumigation is another method used to control insects in stored grain. It involves sealing the grain bin and introducing a gas that permeates the stored crop, killing pests. Grain bin fumigation is dangerous and toxic. It should be conducted by trained and licensed pest control professionals.
Pros of Fumigation:
- High Effectiveness: Fumigation is one of the most effective methods for eradicating a wide range of insect pests in stored grain facilities.
- Minimal Residue: Modern fumigants like phosphine break down rapidly, leaving minimal chemical residue behind that can result in grain residues.
Cons of Fumigation:
- Toxicity Concerns: While fumigants are effective, they are toxic to humans and animals. Fumigation must be conducted by licensed professionals with strict adherence to safety protocols.
- Consumer Concerns: Consumers may fear that fumigants leave harmful residues on food products, even though regulations require that fumigated grain meets safety standards before entering the market.
Safety Basics:
- Fumigants must be applied only by trained and licensed professionals to avoid accidents.
- Workers should use personal protective equipment (PPE) and ensure the area is sealed off to prevent gas leaks.
- Always follow the re-entry interval, the time period after fumigation during which it is unsafe to enter the grain bin.
Residue Concerns:
- Properly applied fumigation, particularly with phosphine, leaves little to no residue on stored grains.
- Grain that has been fumigated must undergo a waiting period before it can be released for processing or sale. This ensures that no harmful chemical residues are present when the grain reaches the consumer.
Economic Impact of Fumigation and Insect Control
The cost of fumigation and insect control methods like insecticides, IGRs and DE can vary depending on the size of the grain bin and the level of infestation. However, the cost of not treating stored grain can be much higher. Insect-damaged grain results in ongoing shrink from loss of dry matter, rejected shipments, reduced market prices, and lower feed quality.
By reducing insect infestations through proper management, farmers can protect the value of their stored crops and maintain the nutritional quality of grain used for feed and food. The investment in insect control can significantly reduce long-term losses and increase profitability across the supply chain of farms, grain distribution centers, milling facilities or feed processors and commercial food storage, distribution and retail outlets to the end consumers.
Key Takeaways for Farmers and Consumers
- Prevention is key: Proper sanitation, drying, and monitoring can prevent many insect infestations before they start.
- Fumigation is safe when done properly: While fumigation uses toxic gases, it leaves minimal residue on grains when applied correctly, making it safe for both feed and food products. Fumigation gases require certified applicators and it is difficult and expensive to find qualified companies for fumigation services in many areas.
- Insecticides and IGRs offer practical and effective alternatives: Products can be applied when filling or emptying grain bins, providing long-term protection against a variety of pests. These methods are often less invasive than fumigation and are easy to integrate into regular grain handling procedures. Chemical residues are minimal and usually considered safe when applied at label recommendations, however, may affect where grain can be marketed, therefore, research is necessary to ensure crop protectant products are acceptable to your buyer. IGRs only affect insects at certain stages of development and do not have negative impacts to humans or other animals.
- Natural Alternatives like diatomaceous earth can be used to keep insect levels at controlled to reduce loss and quality. DE can be added while loading or on top of grain in storage to reduce infestations without leaving harmful residues or having restrictions in marketing the grain.
Conclusion: Choosing the Right Control Method
Effective insect control in grain storage is essential for maintaining grain quality and protecting both the farmer’s investment and the consumer’s trust. Whether through fumigation, insecticides, IGRs, or a combination of methods, each option has its pros and cons. Farmers should assess their individual needs, storage conditions, and pest pressure to choose the best solution.
Consumers can feel confident knowing that stored grains treated with modern pest control methods are subject to strict safety regulations that protect the quality and safety of the food and feed products they rely on. Whether using fumigation, IGRs, or natural alternatives, these solutions help ensure that stored grains remain safe, nutritious, and free of pest damage.
The average loss of stored cereal grains in the U.S. due to insect damage can be significant, both in terms of quantity and economic impact.
Here is a handy resource with charts of chemicals, application information and grain bin capacity:
South Carolina Pest Management Handbook for Field Crops – 2015 307 FARM-STORED GRAIN INSECT MANAGEMENT Robert G. Bellinger, Extension Entomologist
